1、BRITISH STANDARD BS 6556-2: 1985 Incorporating Amendment Nos. 1, 2 and 3 Low speed digital signals for use in coal mines Part 2: Specification for transformer coupling UDC 622.489:621.398.037.37:681.327.8BS6556-2:1985 This British Standard, having been prepared under the directionof the Mining and Q
2、uarrying Requisites StandardsCommittee, was published under the authority ofthe Board of BSI and comes intoeffect on 31 January 1985 BSI 11-1999 The following BSI references relate to the work on this standard: Committee reference MQE/25 Draft for comment 82/76935 DC ISBN 0 580 14209 4 Committees re
3、sponsible for this British Standard The preparation of this British Standard was entrusted by the Mining and Quarrying Requisites Standards Committee (MQE/-) to Technical Committee MQE/25 upon which the following bodies were represented: Association of British Mining Equipment Companies Council for
4、Electrical Equipment for Flammable Atmospheres (BEAMA) Health and Safety Executive National Coal Board National Union of Mineworkers Amendments issued since publication Amd. No. Date of issue Comments 6205 February 1992 6903 April 1992 7935 November 1993 Indicated by a sideline in the marginBS6556-2
5、:1985 BSI 11-1999 i Contents Page Committees responsible Inside front cover Foreword ii 1 Scope 1 2 Definitions 1 3 General conventions 1 4 Data link configurations 1 5 Channel allocation 2 6 Data rate 2 7 Modulation parameters 2 8 Line spectrum 2 9 Modulator 2 10 Demodulator 3 11 System performance
6、 3 12 Cable connections 3 13 Environment 3 14 Line circuit parameters 4 15 Marking 4 16 Documentation 5 Appendix A Cable parameters used for system performance test 13 Figure 1 Simplex operation 5 Figure 2 Duplex point-to-point operation 5 Figure 3 Multi-drop operation 6 Figure 4 Resistive node 7 Fi
7、gure 5 Frequency shift keying (FSK) 8 Figure 6 Originate channel spectrum limits 9 Figure 7 Answer channel spectrum limits 10 Figure 8 Modulator configuration 11 Figure 9 Demodulator configuration 11 Figure 10 Performance test configuration 12 Figure 11 Generator of 511 bit pseudo-random data 12 Fig
8、ure 12 Core configuration of cable 13 Table 1 Manner of modulator operation 2 Table 2 Manner of demodulator operation 3 Table 3 Performance tests 4 Publications referred to Inside back coverBS6556-2:1985 ii BSI 11-1999 Foreword This Part of BS 6556 has been prepared under the direction of the Mining
9、 and Quarrying Requisites Standards Committee. Control and monitoring activities below ground in coal mines require the transmission of data between items of electrical equipment supplied by different manufacturers. Data can be transmitted in analogue or alternatively digital form. For analogue, BS
10、5754:1980 “Specification for electrical analogue and state signals for use in coal mines” was produced with the purpose of promoting compatibility between transducers, recorders, indicators and data transmission systems of different manufacture and having inputs or outputs, as appropriate, in the fo
11、rm of d.c. voltage analogue signals or signals derived from relay contacts or a mechanical switch. This standard deals with the digital form. A major disadvantage with control and monitoring systems employing the direct transmission of analogue signals is that since a galvanic connection is necessar
12、y between the transmitting and receiving circuits, faults, at different points of the system, particularly to earth, can seriously affect overall performance. The avoidance of such faults, on pit-wide systems, is extremely difficult. The generation of analogue signals within high voltage switchgear,
13、 and subsequent transmission for monitoring purposes, also presents difficulty in achieving the required degree of segregation between intrinsically safe and power circuits. A further disadvantage with analogue signals is that the simultaneous transmission of several signals requires either a multic
14、ore cable or separate cables. These disadvantages can be largely overcome if the analogue or state information is transmitted in the form of serially coded digital signals. With such signals complete galvanic isolation between the transmitting and receiving circuits is possible and, within wide limi
15、ts, only two wires are required for transmission in each direction irrespective of the volume of data. If full benefit of digital signal data transmission is to be realized it is important that transmission systems of different manufacture conform to a common electrical standard and operate in a uni
16、form manner with identical procedure (or protocol) for handling the data. This standard aims to promote such conformity. It specifies relevant requirements for a low speed digital signal link comprising a master and one or more slaves which interconnects the intrinsically safe circuits of one item o
17、f apparatus and the intrinsically safe circuits of other apparatus in such a way that units of different manufacture can be interchangeably coupled at the transmission line terminals. This standard is published in three Parts as follows: Part 1: Specification for optical coupling; Part 2: Specificat
18、ion for transformer coupling; Part 3: Specification for message protocols. Parts 1 and 2 of this standard offer alternative methods of achieving galvanic isolation between the intrinsically safe circuits of interconnected apparatus, but the two methods are not compatible. Part 1 of this standard spe
19、cifies a 600 bits/s transmission system which employs optical coupling as the means of achieving galvanic isolation. A system will comprise a master and from 1 to 8 slaves connected in point-to-point or multi-drop modes, with two cable conductors being used for each direction of transmission. Transm
20、ission from the master to a slave is achieved by the master acting as a switched current source which activates a light emitter at each slave. Transmission from slave to master is achieved by the master acting as both a current source, which is switched at the slave by a light dependent device, and
21、a current monitor which senses the switched current.BS6556-2:1985 BSI 11-1999 iii This Part of this standard specifies a 600 bits/s transmission system which employs transformer coupling as the means of achieving galvanic isolation. A system will comprise a master and from 1 to 15 slaves connected i
22、n point-to-point. or multi-drop modes. Transmission between master and slaves is achieved by frequency shift keying (FSK) techniques, one pair of cable conductors being used for each direction of transmission. Part 3 of this standard defines the message protocols to be used by systems complying with
23、 Parts 1 or 2. It does not, however, place any restrictions on the application data contained in transmitted messages, although industry standards may exist to regulate this. It is envisaged that for high voltage applications optical coupling will be employed due to the relative ease of meeting segr
24、egation requirements. The optical system, however, has a limit of 8 slaves and a range of 2 km while the transformer method has a greater range and can handle up to 15 slaves. For intermediate applications either system may be suitable. In Parts 1 and 2 of this standard, slaves are the physical inte
25、rface between the transmission line and one or more addressable logical slaves specified in Part 3 of this standard. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a
26、British Standard does not of itself confer immunity from legal obligations. Attention is drawn to the Health and Safety at Work etc. Act 1974, the Mines and Quarries Act 1954, the Regulations made under these Acts, and also any other appropriate statutory requirements or byelaws. These place respons
27、ibility for complying with certain specific safety requirements on the manufacturer and the user. The address of the recognized certification authority in the United Kingdom for Group 1 (coal mining) apparatus for intrinsic safety purposes is as follows: Health and Safety Executive HSE (M) Certifica
28、tion Support Unit Harpur Hill, Buxton, Derbyshire SK 17 9JN. Summary of pages This document comprises a front cover, an inside front cover, pagesi toiv, pages1to14, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. Th
29、is will be indicated in the amendment table on the inside front cover.iv blankBS6556-2:1985 BSI 11-1999 1 1 Scope This Part of BS6556 specifies the electrical input and output characteristics for the transformer coupling of intrinsically safe transmitting and receiving circuits for use in coal mines
30、. These form a low speed digital data transmission link in which data is transmitted using frequency shift keying techniques. A data transmission system comprises a master and up to15physical slaves. The circuits of all stations are galvanically isolated from the line circuits by transformers. NOTE
31、1Each physical slave may support more than one addressable logical slave as specified in Part 3 of this standard up to a maximum of 15addressable slaves for the complete system. This Part of BS 6556 only applies to apparatus where the circuits connected to the transmission lines are designed to be i
32、ntrinsically safe in accordance with BS 1259, BS 5501-7 or BS 5501-9 as appropriate. NOTE 2Where apparatus, which is intended to be used in potentially explosive atmospheres, contains other circuits which are not intrinsically safe, those circuits will have to be given an alternative form of protect
33、ion in accordance with BS 229, BS4683 or BS 5501 as appropriate. NOTE 3The titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS 6556 the following definitions apply. 2.1 duplex the transmission of data simultan
34、eously in opposite directions through a system 2.2 simplex the transmission of data in one direction only 2.3 bit the element of digital information taking the value1or 0 2.4 binary having only two states (of numbers). A system of numbering where each digit has only two possible values, 0 or 1 2.5 c
35、hannel a circuit carrying information in one direction 2.6 MODEM a combined modulator demodulator 2.7 ready for sending (RFS) an output from the modulator 2.8 receive line signal detected (RLSD) an output from the demodulator 2.9 request to send (RTS) a control input of the modulator 2.10 frequency
36、shift keying (FSK) a method of transmitting information by different frequencies 2.11 dBm power level referenced to 1 mW 2.12 isochronous distortion deviation of received bits from their nominal period expressed as a percentage of the nominal bit period 3 General conventions The following convention
37、s shall apply: a) space = value 0 = low frequency = start; b) mark = value 1 = high frequency = idle. 4 Data link configurations 4.1 General The data link shall allow data to be transmitted between a master and up to 15 slaves. Each transmitting and receiving station shall be galvanically isolated f
38、rom the transmission lines by coupling transformers. NOTEThe connections between the transformer and the transmission line may have to include safety components to meet the requirements of clause 14. The modulator and demodulator shall be inter-connected to form data links in the following ways: a)
39、point-to-point simplex using a single twisted pair transmission line (see Figure 1); b) point-to-point duplex using a two-pair or twisted quad transmission line (see Figure 2); c) multi-drop duplex using a two-pair or twisted quad transmission line with up to 15 slaves (seeFigure 3).BS6556-2:1985 2
40、BSI 11-1999 4.2 Termination rules In multi-drop configuration the following line termination rules shall apply. a) When the transmission line is looped into each MODEM, all MODEMs, except those at each end, shall have the line termination switched out. The end MODEMs shall have the line termination
41、switched in. b) Where the length of a spur is less than 1 km the line termination of MODEMs on the spur shall be switched out. c) Where the length of a spur is greater than1km, the node shall be a symmetrical resistive splitter (see Figure 4). In this case the final MODEM on each spur shall have the
42、 line termination switched in. All other MODEMs on the spur shall have the line termination switched out. d) Impedance switching in any one MODEM on both modulator and demodulator line terminations shall be by a single actuator. 5 Channel allocation Transmission from master to slave shall be via the
43、 originate channel. Transmission from slave to master shall be via the answer channel (see Figure 1 and Figure 2). For multi-drop operation the channel allocation shall be the same but with multiple slaves (see Figure 3). 6 Data rate The data rate shall be 600 bits/s 0.1 %. 7 Modulation parameters T
44、he modulation method shall be phase continuous frequency shift keying (FSK) (see Figure 5). The master modulator and slave demodulator shall operate in the following frequency band: originate channel: 1170 100 Hz, i.e.mark1270 Hz, space 1070 Hz. The master demodulator and slave modulator shall opera
45、te in the following frequency band: answer channel: 2 125 100 Hz, i.e.mark2225Hz, space 2025 Hz. The tolerance on the centre frequency, i.e. 1170 Hz or 2125 Hz shall be 5 Hz. The tolerance on the difference between mark frequency and space frequency shall be 10 Hz. 8 Line spectrum The spectrum of th
46、e transmitted signal with the line termination switched in and with 600 7 connected across the line terminals shall comply with Figure 6 for the originate channel and with Figure 7 for the answer channel. 9 Modulator 9.1 General The modulator shall accept serial binary data at the specified data rat
47、e and convert it to audio frequency signals for transmission via a transformer to line (see Figure 8). The modulator shall be controlled by the interface signal “request to send” (RTS) and shall output the signal “ready for sending” (RFS). 9.2 Transmit levels The transmitted signal measured at the l
48、ine terminals with the line termination switched in and with 600 7 connected across the line terminals shall be 0 1 dBm. 9.3 Modulator line interface The interface between the modulator and the transmission line shall be a transformer to provide galvanic isolation and a balanced line signal (seeFigu
49、re 8). The transformer shall be designed such that the line terminals have intrinsically safe segregation from the power supply of the apparatus. The modulator shall be operated in current driving mode and present an impedance to the line in excess of 5 k7. Means shall be provided for terminating the line with an impedance of 600 7 10 % (see4.2). The degree of balance of the transformer at the line terminals shall be better than 40 dB. 9.4 Ready for sending delay The modulator shall operate the RFS signal in response to changes in
